sackcloth

of Hebrew origin (שַׂק); "sack"-cloth, i.e. mohair (the material or garments made of it, worn as a sign of grief):-- sackcloth.

from שָׁקַק; properly, a mesh (as allowing a liquid to run through), i.e. coarse loose cloth or sacking (used in mourning and for bagging); hence, a bag (for grain, etc.); sack(-cloth, -clothes).